It is well known to attach a variety of rigs such as hydraulically operated rigs above a wellhead. For example, snubbing units are known in the oil and gas industry for facilitating access to a well which is under pressure including, for example, well operations such as well completions. A snubbing unit includes structure and equipment above a wellhead for manipulating tubular components such as pipe, tubing, and bottom hole assemblies (BHA) in and out of a well while controlling the well under pressure.
Generally, a snubbing unit employs stationary (lower) and traveling (upper) slip assemblies, opposingly oriented, to releasably and controllably shift tubular components into and out of the well through a wellhead despite the possibility of either heavy tubular loads, which urge the tubular components to fall into the well, or the pressure-generated forces on the tubular components, which urge the tubular components out of the well. The snubbing unit is installed above an existing wellhead seal, such as that created by a blow-out preventer (BOP), and incorporates its own seals to seal the tubular components as they are introduced or removed from the wellhead, such as through the use of a stripping head.
Most conventional snubbing units fall into either rig-assisted or self-contained units. Rig-assisted snubbing units are typically snubbing units that are pivotally mounted to a truck and require assistance by an onsite service rig so as to winch them upright, pivoting from the truck, to a snubbing position over the wellhead. Self-contained units are typically transported to site on a truck and lifted into position, over the wellhead, by a separate crane unit. During operations, self-contained snubbing units do not require the assistance from an on-site rig.
When snubbing in low-pressure well environments, such as wells with surface pressures under 12,000 kPa, a compact, rig-assisted snubbing unit is often the ideal choice. A compact snubbing unit can be easily transported to the well site, such as in a 1 ton pickup truck, and is practical and cost effective for single wells and underbalanced drilling. Additionally, a compact snubbing unit reduces or eliminates viewing obstructions often experienced by service rig operators when utilizing traditional (larger) sized snubbing units. One example of a compact snubbing unit is the one marketed under the trade-mark MINI BRUTUS by Team Snubbing Services Inc. of Rocky Mountain House, Alberta, Canada.
Despite the many advantages of a compact snubbing unit, the set-up of such a unit still requires the snubbing unit to be installed above an existing wellhead seal and to incorporate its own seals to seal the tubular components as they are introduced or removed from the wellhead. Typically a compact snubbing unit, such as the MINI BRUTUS™, is installed above a blow-out preventer (BOP) and incorporates an RS-100 stripping head as its seal to seal the tubular components.
Push/pull systems or push/pull units are also known in the art and are used to manipulate tubular components in and out of a well. Push/pull units provide alternatives to, and/or improvements over, conventional snubbing systems. Such push/pull systems are generally mounted at the rig floor (e.g. on the rotary table) and, therefore, allow live well operations to be conducted at the rig floor rather than in the greatly elevated work baskets as is generally the case with conventional snubbing units. One example of a push/pull system is that manufactured by Tesco Corporation of Calgary, Alberta, Canada.
However, the prior art push/pull system manufactured by Tesco Corporation is cumbersome, large and heavy, does not have the compactness that has become associated with compact snubbing units such as the MINI BRUTUS™ and cannot be used to retrofit such compact snubbing units and/or convert such units into a push/pull system.